ATR (“ATM and Rad3 related”) kinase is a protein kinase involved in cellular responses to DNA damage. ATR kinase acts with ATM (“ataxia telangiectasia mutated”) kinase and many other proteins to regulate a cell's response to DNA damage, commonly referred to as the DNA Damage Response (“DDR”). The DDR stimulates DNA repair, promotes survival and stalls cell cycle progression by activating cell cycle checkpoints, which provide time for repair. Without the DDR, cells are much more sensitive to DNA damage and readily die from DNA lesions induced by endogenous cellular processes such as DNA replication or exogenous DNA damaging agents commonly used in cancer therapy.
Healthy cells can rely on a host of different proteins for DNA repair including the DDR kinase ATR. In some cases these proteins can compensate for one another by activating functionally redundant DNA repair processes. On the contrary, many cancer cells harbour defects in some of their DNA repair processes, such as ATM signaling, and therefore display a greater reliance on their remaining intact DNA repair proteins which include ATR. In addition, many cancer cells express activated oncogenes or lack key tumour suppressors, and this can make these cancer cells prone to dysregulated phases of DNA replication which in turn cause DNA damage.
ATR has been implicated as a critical component of the DDR in response to disrupted DNA replication. As a result, these cancer cells are more dependent on ATR activity for survival than healthy cells. Accordingly, ATR inhibitors may be useful for cancer treatment, either used alone or in combination with DNA damaging agents, because they shut down a DNA repair mechanism that is more important for cellular survival in many cancer cells than in healthy normal cells. In fact, ATR inhibition has been shown to be effective in cancer cells as single agents and as potent sensitizers to radiotherapy and genotoxic chemotherapy.
Additionally, ATR is also implicated in other diseases, such as HIV1: (see Ward et al, 2009 PLOS Pathogens 5:e1000613, Lai et al, 2005 J Virol 79:1544, and Daniel et al 2003 PNAS 100:4778); Hepatitis B (see e.g., Zhao et al, 2008 World J Gastroenterol 14:6163, Wang et al 2008 JBC 283:25455); Adenovirus (see e.g., Nichols et al, 2009 J Virol 83: 5987), and Psoriasis (see e.g., Derheimer et al., 2009 Mol Pharmacol 75:599).
Accordingly, there is a need for the development of potent and selective ATR inhibitors to treat these diseases. More specifically, there is a need for the development of potent and selective ATR inhibitors for the treatment of cancer, either as single agents or as combination therapies with radiotherapy or genotoxic chemotherapy.